In general, electric power supply systems for supplying power to various kinds of loads arranged on a floor surface can be broadly classified into contact-type power supply systems which supply power by bringing the electrodes provided so as to be exposed on the floor surface into contact with the electrodes provided on the bottom surface of the load; and noncontact-type power supply systems which supply power without bringing the electrodes provided in a non-exposed matter inside of the floor into contact with the electrodes of the load.
Among them, a conventional noncontact-type electric power supply system is disclosed in Patent Document 1, for example. This system performs electric power supply to a load (ground mobile body) that moves along a guideway, and is configured to arrange an induction line along the guideway, as well as provide an iron core around which a coil is wound to the ground mobile body. Further, a high-frequency electric current is passed through the induction line so as to perform electromagnetic induction, in which this induction line is set as a primary side, and the coil is set as the secondary side, thereby supplying power to the ground mobile body.
As another noncontact-type electric power supply system, a wireless electric power transmission sheet is disclosed in Non-Patent Document 1. With the use of printing technology, this wireless electric power transmission sheet is configured by forming, on a plastic film, coils for power transmission, MEMS (Micro Electro Mechanical Systems) switches for electric power control, position detection coils for an electric power reception device, and organic transistors for performing position detection with the use of the position detection coils. In this wireless power-transmission sheet, the organic transistor detects a change in the inductance of the position detection coil which accompanies the approaching of an electronic device to the sheet, thereby specifying the approach position of the electronic device. Then, the power transmission coil corresponding to the identified position is selected by the MEMS switch to transmit electric power from the selected power transmission coil.
However, with such a conventional noncontact-type power supply system, there are many limitations in terms of the position, such as it is necessary to align the induction line and the coil so as to bring the induction line and the coil into proximity with each other and to cause the magnetic flux generated by energization of the induction line to pass through the central axis of the coil, in order to raise the power transmission efficiency. Therefore, there have been problems in that it is only possible to supply power along a fixed path such as a guideway, and it is not possible to supply power to a mobile body such as a robot that is required to freely move on the floor surface. In addition, there have been problems in that it is required to use a magnetic body such as an iron core in order to form a magnetic path, and thus the weight increases, and when the magnetic body is excited by alternating current, magneto-striction occurs and generates noise. In addition, in order to enhance the electric power transmission efficiency with the conventional wireless electric power transmission sheet, it is necessary to align the position of the electric power transmission coil and the position of the electric power reception coil of the electronic device, and nonetheless has many limitations in terms of the position. Furthermore, since many switches are used, there has been a possibility of the reliability declining. Other than the above, it may be possible to consider supplying power with electromagnetic waves as a noncontact-type electric power supply system; however, there are strict regulations from the perspective of avoiding adverse effects on the human body and malfunction of electronic devices, and thus it has been difficult to introduce into an inhabited place such as an office space.
In view of such points, the inventors of the present application and others have proposed an electric power supply system using electric field coupling technology which can contactlessly supply electric power by making use of series resonance or parallel resonance without electromagnetic induction or electromagnetic waves (see Patent Document 2).    Patent Document 1: Japanese Unexamined Patent Application, Publication No. H09-93704    Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2009-89520    Non-Patent Document 1: “Nature Materials”, Vol. 6, p.p. 413-417 (T. Sekitani et al., 2007)